Space junk: Hunting zombies in outer space

Video: Satellite smash

If we don’t deal with orbital debris, Earth will one day have rings of refuse – and we’ll be cut off from space

EARTH’S rings have never looked so beautiful, you think as you look up at the pallid sliver of light arcing through the night sky. Yet unlike Saturn’s magnificent bands of dust and rubble, Earth’s halo is one of our own making. It is nothing but space junk, smashed-up debris from thousands of satellites that once monitored our climate, beamed down TV programmes and helped us find our way around.

This scenario is every space engineer’s nightmare. It is known as the Kessler syndrome after Donald Kessler, formerly at NASA’s Johnson Space Center in Houston, Texas. Back in 1978, he and colleague Burton Cour-Palais proposed that as the number of satellites rose, so would the risk of accidental collisions. Such disasters would create large clouds of shrapnel, making further collisions with other satellites more likely and sparking a chain reaction that would swiftly surround the Earth with belts of debris. Orbits would become so clogged as to be unusable and eventually our access to space would be completely blocked.

On 10 February 2009 it started to happen. In the first collision between two intact satellites, the defunct Russian craft Kosmos-2251 struck communications satellite Iridium 33 at a speed of 42,100 kilometres per hour. The impact shattered one of Iridium 33’s solar panels and sent the satellite into a helpless tumble. Kosmos-2251 was utterly destroyed. The two orbits are now home to clouds of debris that, according to the US military’s Space Surveillance Network (SSN), contain more than 2000 fragments larger than 10 centimetres. The collision may also have produced hundreds of thousands of smaller fragments, which cannot currently be tracked from Earth.

Such debris is a serious worry. With satellites travelling at tens of thousands of kilometres per hour, any encounter with debris could be lethal. “Being hit by a 1-centimetre object at orbital velocity is the equivalent of exploding a hand grenade next to a satellite,” says Heiner Klinkrad, head of the space debris office at the European Space Agency in Darmstadt, Germany. “Iridium and Kosmos was an early indication of the Kessler syndrome.”

Space junk isn’t just made up of dead satellites. It also includes spent upper-stage rockets, used to loft the satellites into orbit, and items that have escaped the grasp of butterfingered astronauts, such as the glove Ed White dropped in 1965 as he became the first American to walk in space, and the tool kit that slipped from Heide Stefanyshyn-Piper’s hand during a 2008 space walk. Protective covers and the explosive bolts used to separate them from uncrewed spacecraft have also been left to float away, along with a few lens caps for good measure. Some of these objects re-enter the atmosphere and burn up, but most are still up there.

The SSN has catalogued 12,000 objects in Earth orbit that are at least 10 centimetres in size, about three-quarters of which are space junk. For objects bigger than 1 centimetre, the estimates are frightening&colon; there are anything from hundreds of thousands to millions of them, mostly in unknown orbits and each capable of smashing a satellite to smithereens. Every rocket launch creates yet more space debris, edging us ever closer to the Kessler syndrome becoming a reality.

Graveyards and zombies

So what can be done? For a start, we can try not to make the problem worse. This can be as simple as ensuring that protective covers are tethered to spacecraft rather than jettisoned. It also includes sticking to international guidelines intended to minimise new debris, drawn up by the Inter-Agency Space Debris Coordination Committee (IADC), which represents all the world’s major space agencies. These require, for example, that spacecraft in low Earth orbit must be made to re-enter the atmosphere and burn up within 25 years of finishing their missions.

Communications satellites in the high-altitude geostationary orbit cannot be brought down practically. Instead, the guidelines say operators should use the last of their satellites’ fuel to boost them into a “graveyard orbit” 300 kilometres higher up (see diagram). Yet even with these guidelines in place, Klinkrad says, “It is pretty common to leave your spacecraft stranded.”

Twelve satellites in geosynchronous orbit failed in 2008, but only seven were boosted in accordance with the guidelines. And more than 800 of the 1200 trackable objects near the geostationary corridor are not active satellites. The most recent drama there involved the communications satellite Galaxy 15, which became widely known as the “zombie satellite” (see “March of the zombie”).

Even if the guidelines were followed to the letter, the number of debris fragments would still go up. “We could even stop launching and the amount of debris would still rise,” says Hugh Lewis of the University of Southampton in the UK. That’s because accidental collisions would still happen.

Kessler predicted that if nothing were done to remove debris, we would begin to suffer the consequences in 2000. As it turned out, the Iridium and Kosmos collision did not happen for another nine years. The main reason for our period of grace may be that modern satellites are manoeuvrable. When a piece of space debris is seen approaching, satellite operators can move their “bird” out of the way.

Such ducking and dodging used to be rare. Not any longer. A few years ago, operators were receiving one or two warnings of space debris a month; now it can be two or three times a week. Every time a new warning comes in, they must begin a 72-hour tracking campaign using ground-based radar to refine the orbit of the object and establish whether to take evasive action or not.

“A few years ago, we were receiving one or two warnings of space debris a month. Now it’s three a week”

As if accidents weren’t bad enough, in 2007 China launched a missile that destroyed their Feng Yun 1C weather satellite. It was an ostentatious display of military capability, perhaps intended as a warning to anyone thinking of putting weapons into space, but it also sent shock waves through space operations centres around the world. That incident, in combination with the Iridium smash in 2009, created so much debris that the number of fragments in low Earth orbit large enough to be tracked from the ground almost doubled.

Some craft are more vulnerable to debris than others, says Lewis, who has developed software to model how space junk spreads and evolves over time. Take the A-train – four satellites that orbit Earth one behind the other, monitoring the atmosphere as they go. The closest pair are just 15 seconds apart, and this proximity makes the A-train especially vulnerable. Should one of the A-train’s units be smashed by an incoming piece of debris, the chances are we could lose all four.

As things stand, remediation – as space engineers call it – is a necessity. In other words, someone will have to go up there and bring the stuff down. But which bits? Who will do it? How will they do it? And who is going to pay?

Initially the temptation might be to bring down as much as we can, but this will cost. “It will be so expensive to remove satellites from orbit that you will have to target which ones you want to take down,” Lewis says. He has investigated a number of approaches that aim to identify the most dangerous space junk. The most obvious strategy might be to target the biggest objects, but Lewis’s analysis shows that this may not be best. Just because something presents a large target does not mean that it would imperil other satellites. It may be that a smaller defunct satellite in a particular orbit presents more danger to a greater number of live craft.

To make this idea more tangible, Lewis is treating satellites and space junk as elements in a kind of mathematical network, a network whose connections reveal how many objects a given satellite approaches in orbit (Acta Astronautica, vol 66, p 257). “It is like Google page-ranking. The most connected objects come up near the top of the list,” says Lewis.

These orbital connections can be used to decide which objects are the most dangerous. Bring those down and you halt the Kessler syndrome in its tracks. Lewis won’t be drawn on which bits of junk are the most dangerous, however; he is loath to rile their owners.

A range of new technology could be used to bring down dead satellites, Lewis says, and it would itself be satellite-based. A specialised satellite could fire a laser at a derelict craft, melting components and releasing gas that would propel it out of harm’s way. Or the clearance satellite could play an orbital game of “pin the tail on the donkey”, attaching tethers to the dead satellite to increase atmospheric drag and cause it to burn up in the atmosphere.

On the face of it, every country ought to welcome the development of new technology to clean up space. In reality, the picture is clouded by the obvious military applications. “If you can bring down dead satellites, you can bring down live ones too,” Lewis says.

Space bounty

Then there are the legal issues around space debris. Under maritime law, anyone can remove an abandoned ship without the owner’s permission. Not so for space vehicles, as stipulated in the 1967 Outer Space Treaty. “Once you put it up there, it is yours for life,” says James Dunstan, a lawyer specialising in issues to do with space and founder of Mobius Legal Group in Washington DC. So the US may not remove a Russian satellite from orbit with impunity, even if that satellite were completely dead and presenting a danger to working spacecraft.

Together with Berin Szoka of the Progress and Freedom Foundation, a think-tank also based in Washington DC, Dunstan has created the outlines of an economic model that would see private industry taking responsibility for removing space debris. An international body, such as the IADC, would put a price – rather like a bounty – on every defunct satellite. Private companies can lodge bids with satellite owners for the right to buy and de-orbit their spacecraft. Once de-orbiting is successfully completed, the company could pocket the bounty, which would be funded out of a new tax that satellite operators would have to pay.

But why bring these things down just to burn up in the atmosphere when they are potentially valuable? Dunstan estimates that of the 6000 tonnes of material in Earth orbit, one-sixth is high-grade aluminium in the form of discarded upper rocket stages. These empty fuel tanks have an internal volume 20 times that of the International Space Station. If they could only be corralled, they would make an inexpensive space station or, Dunstan suggests, they could be cut into shielding material to protect other satellites. “Why not set up Joe’s Shingle Shack in orbit?” he asks, only half-joking.

While the orbital equivalent of a used-car salesman selling satellite parts is some way off, the need to do more about space junk is immediate. “Our future ability to use space is directly jeopardised by space debris,” says Szoka. Encouragingly, the European Space Agency has signed a contract with Spanish company Indra Espacio to develop a radar system to track space debris. In the US, Ball Aerospace and Technologies has collaborated with Boeing on the Space Based Space Surveillance satellite, a dedicated space-junk telescope awaiting launch.

“It is very urgent that we begin to remove mass from orbit,” says Klinkrad. Even as we talk, his team is beginning another tracking campaign. Something is stalking ESA’s ERS-1 satellite, and they have to decide in the next day or two whether or not to use precious fuel to move the spacecraft. As Klinkrad says in a resigned voice, “This is becoming an everyday situation.”

March of the zombie

Galaxy 15 is a name to strike terror into the hearts of satellite operators around the world. Once an ordinary and largely anonymous telecommunications satellite, it is now a zombie. It stopped talking to its masters on 5 April, just as a solar storm battered the Earth.

The satellite’s owner Intelsat is still investigating whether this caused Galaxy 15 to lose its mind. But Galaxy 15 is not only a problem for its owner. Following its malfunction, it began an inexorable march across space, bound for a natural orbital graveyard created by Earth’s gravity. In its blind stumble to get there, Galaxy 15 risks colliding with other satellites. It has already menaced three and has at least three others in its path. To avert destruction, satellite operators must wait for the zombie to draw close and then manoeuvre their own satellite to “leapfrog” it.

What makes Galaxy 15 particularly annoying is that its main transmitter and receiver are still working. As it drifts across the path of another working satellite, it could interfere with communications. To avoid this, satellite operators are signalling on tighter beams with larger antennae and less power. In effect they are whispering to their satellites in the hope they won’t attract the zombie’s attention.

All of this is costing money – big money. “These satellites are profit centres making millions of dollars a month,” says James Dunstan of Mobius Legal Group in Washington DC. Every dodge to avoid a collision eats around &dollar;10 million into a satellite’s profits. That’s because collision avoidance manoeuvres waste precious fuel that would otherwise be used to combat the tendency for satellites to drift off into orbital graveyards. Although companies do not divulge how much fuel they use in collision avoidance manoeuvres, Dunstan estimates that each one must shorten a satellite’s lifespan by between four and 12 months. He says dealing with Galaxy 15 could easily cost the telecomms industry &dollar;100 million.

Tobias Nassif of Intelsat sees it differently. He says that constant vigilance means that most collision manoeuvres can be built into ones made fortnightly to stop satellites drifting. “Space debris is not a grave concern,” he says, “but it is always on our mind.”

By Stuart Clark

Stuart Clark is author of The Big Questions&colon; The Universe (Quercus, 2010). Find his blog at www.stuartclark.com